Research suggests that bright light plus company may be the best
Rx for females with SAD

By Diane Swanbrow
News and Information Services

Marcia Governale with one of the degus used in the
experiments. Photo by Bob Kalmbach

Working with an unusual colony of South American rodents called degus
(day-goos), U-M researchers have discovered striking sex differences
in how quickly the creatures reset their biological clocks in
response to changes in light and social contact.

The discovery could lead to different ways of helping men and
women who suffer from seasonal affective disorder (SAD), jet lag,
shift work problems and other disruptions in their circadian rhythms.

Male degus shift their body temperature and activity cycles more
quickly than females when exposed to light cues alone. However,
females resynchronize their internal clocks much faster if they're
also getting social cues from other females who've already made the
changes.

For the research, biopsychologist Theresa M. Lee and graduate
students Marcia Governale and Namni Goel conducted a series of
experiments with Octodon degus, a small diurnal rodent well-suited
for research on circadian, or daily, rhythms. They have body
temperature and physical activity cycles similar to people. They're
also social animals with individual as well as male-female
differences in adapting to circadian changes.

"We know that the circadian rhythms of men and women differ," says
Lee, an associate professor. "But there's very little good research
on the reasons. Our work with degus suggests that males and females
may have different levels of sensitivity to different kinds of
environmental synchronizing cues."

For one set of studies, Lee and associates analyzed how long it
took male and female degus to readjust to six-hour advances and
delays in the 24-hour light-dark cycle. When the animals were housed
alone, males readjusted faster than females. When females were housed
with other females who had already adapted to the new light-dark
cycle, however, their recovery rate increased by 30 percent to 40
percent.

Male "phase-shifters" showed no sensitivity to cues provided by
animals of either sex, a finding that might not surprise
misanthropists.

"In most species of vertebrates, the light-dark cycle is the most
important environmental cue for resetting the circadian clock," notes
Governale. "But there are other cues as well, many of them involving
social behavior. Birds resynchronize activity cued by song alone,
with light and temperature held constant. Bats are influenced by the
activities of other bats."

To find out what it is about the social cues female degus give
each other that enhances their ability to shift phases, Governale
conducted a series of studies slightly different from the first
studies, in which the animals had either been housed alone or housed
in the same cage, separated from each other by a screen.

Governale put female degus who were on different circadian cycles
into separate environmental chambers linked by an air hose that
pumped air from the chamber occupied by an already-adjusted "donor"
into the box of the female phase-shifter. Female degus who could
smell another female already on the new cycle changed to a new cycle
themselves 39 percent faster than those reacting to light cues alone.

It's a far cry from degus to people, Lee cautions. Still, the line
of research suggests a way to enhance the effectiveness of bright
light treatment for women who find themselves becoming sleepier,
hungrier and more depressed as the Dec. 21 winter solstice
approaches.

Don't just go outside, or keep the lights turned on while you're
in. Seek out the company of women friends who are not chronically
sleepy, hungry or depressed. They may be way ahead of you.